Hydraulic control system for agricultural implements

ABSTRACT

A control mechanism for agricultural implements mounted on three-point linkages in tractors includes a valve mechanism which controls the hydraulic circuit. A single selection and operational control device operates the implements and draft- and position-sensing means act through a cam and lever arrangement for controlling the operation of the valve mechanism which includes two concentrically arranged valve members for regulating the flow of the fluid in the hydraulic circuit.

United States Patent Inventors Chandra Mohan;

Gursharan Singh Rihal; Balbir Singh Devgun, all of Durgapur, India Appl. No. 822,252 Filed May 6, 1969 Patented Oct. 19, 1971 v Assignee Council 01 Scientific and Industrial Research New Delhi, India Priority July 29, 1968 Great Britain 36,05 l/68 HYDRAULIC CONTROL SYSTEM FOR AGRICULTURAL IMPLEMENTS 26 Claims, 8 Drawing Figs.

US. Cl 172/9, 137/614.l6 lnt.Cl At 11b 63/112, (305d 1 1/00 Field of Search 172/9, 7,

[56] References Cited UNITED STATES PATENTS 2,608,954 9/1952 Hogan 137/6l4.l6 X 2,799,251 7/1957 Newgen 172/9 X 2,921,638 l/196O Dushane 172/448 X 3,142,342 7/1964 Bruonak et al. 172/9 3,203,176 8/1965 Zeek 137/637.2X 3,489,224 1/1970 Bunting 172/9 Primary ExaminerRobert E. Pulfrey Assistant ExaminerStephen C. Pellegrino AttorneyMcGlew and Toren ABSTRACT: A control mechanism for agricultural implements mounted on three-point linkages in tractors includes a valve mechanism which controls the hydraulic circuit. A single selection and operational control device operates the implements and draftand position-sensing means act through a cam and lever arrangement for controlling the operation of the valve mechanism which includes two concentrically arranged valve members for regulating the flow of the fluid in the hydraulic circuit.

PATENTEnum 19 1971 3. 6 l 3 7 98 SHEET 1 BF 7 Inventor: a-m'i fimm. Bm-Im man vavwu hwww'lf Attorneys PATENTEUUET 19 197i SHEET 5 BF 7 CHFINDRH 6085"?) ima: y

HYDRAULIC CONTROL SYSTEM FOR AGRICULTURAL IMPLEMENTS This invention relates to the hydraulic system and allied controls provided on tractors for working implements of the mounted type, such tractors being provided with the wellknown three-point linkage and single-acting hydraulic ram for lifting, holding and lowering the implements.

The purpose of this invention is to effectively and conveniently control the working depth of the implement by a single operating lever, a new type of control valve and associated linkage, necessary feedback system and a pump combination with the same.

It is customary in tractors of the type described above to have provisions whereby the working depth of the implement can be controlled by the driver from his seat. Two different control arrangement are usually provided. In position control." the position of the three-point linkage and consequently the working depth of the implement is dependent upon the position of the operating lever in its position control" range and each position of the operating lever corresponds to a known working depth to the implements. In draft control," each position of the operating lever in its draft control range corresponds to a particular soil draft of the implement and the draft is maintained at the value set on the operating lever irrespective of varying conditions of soil, the implement moving up or down in the soil automatically for maintaining the soil draft at the set value.

Known hydraulic systems are either adapted for control of the suction side (low-pressure side) of a pump or the discharge side (high-pressure side) of a pump. This invention relates particularly to a control mechanism adapted for operation on the suction side of a pump.

Known suction systems usually incorporate a single control valve actuated by the operational means through a hinged floating lever, the responsive means being connected to the hinge of the said floating lever. By these means, the control valve is actuated by the operational means in one direction to either cause the entry or the discharge of high-pressure fluid to the hydraulic cylinder, the responsive means connected to the hinge point serving to actuate the value in the reverse directions; the said control valve reaching its neutral position when both entry into and discharge from the hydraulic,

cylinder are blocked at which stage the three-point linkage has achieved the setting corresponding to the setting of the operational means.

Known systems both on the suction and on the discharge side incorporate two or more independent selection or operational means or selection and operational means. The disadvantage of such a system is that it necessitates an operator to work on two or more operational means A drawback of known systems is their complicated design and the inconvenience to the driver in having to manipulate two or more operating and selection levers.

According to this invention there is provided a mechanism for the regulation of hydraulic circuits in tractors for controlling the movement and working of mounted implements attached to the three-point linkage, comprising a valve mechanism controlling the working of the said hydraulic circuit, a single selection and operational control means for providing selective working of the said implement and controlling its working and, a responsive means provided and adapted to receive an actuation movement from the implement through actuation draftand positionsensing means, said responsive means also adapted to receive an actuation from said selection means, said valve mechanism comprising at least a first and second control valve disposed therein, said second valve disposed within said first valve, the said first valve being actuated by the said selection and operational means and the said second valve being capable of actuation by the responsive means.

This invention which is a control mechanism for a tractor having a hydraulic actuator for raising and lowering implements includes a control valve" constituted of two concentric valves termed hereafter as the spool valve and the annular sleeve valve, means for actuating one of these valves from the operating lever and the other from the feedback signals which could be received either from the draft or position sensors, means whereby the valve movement is connected to either the position or the draft sensors automatically depending upon whether the operating lever is in its position control" or draft control range," means for protection of the system against overloads and faulty operation and, means for varying system response.

The invention makes a fundamental departure from known systems in the control valve," where the operating lever and the feedbacks independently operate the annular sleeve and the spool valves and the operational conditions of the control valve is dependent upon the instantaneous relative position of the spool and the annular sleeve valves. Another feature of the invention is the automatic switchover of the operating means for one of the valves from the position to the draft feedback sensors as the main operating lever is moved over from its position control range to the draft control range and vice versa and, the arrangements provided therein for system protection. Another new introduction is in that the selection of position or draft working and the working depth of the implement both in position and draft control and also the working of single-acting external rams are all effected with a single operating lever, which goes towards more convenient operator handling of the tractor.

The working of the invention is now explained with the help of diagrams where;

FIG. 1 is a schematic view of the rear end of a tractor fitted with the invention in conjunction with the three-point linkage;

FIG. 2 is a sectional view of the main control valve;

FIG. 3 shows the operating lever and its sector with the vari ous operating ranges;

FIG. 4 shows the working of the system in automatic draft control;

FIG. 5 shows the working of the system in position control;

FIG. 6 shows the arrangement of the central cam;

FIG. 7 shows the overload relief arrangement;

FIG. 8 shows another embodiment of the overload relief engagement.

In FIG. 1, single-acting piston 2 works in hydraulic cylinder 1 and actuates lift shaft 3, to the ends of which are attached radial lift arms 4 directed rearwardly. Radial lift arms 4 are connected to the forwardly converging lower links 6 of the three-point linkage through lift rods 5, one of which is ad justable. Upper link 7 of the three-point linkage is provided with the draft sensor spring assembly 9 which provides the feedback for draft. The three-point linkage carries implement 8. The draft sensor spring assembly 9 is bolted to the rear end of the tractor, the connections to the spring being so arranged that it responds to both compressive and tensile forces in the upper link. A helical spring is typically used as the sensor spring, but any other type of spring, viz flat, volute, torsion bar etc. could be adapted for use. The position feedback." signal is obtained from cam 10 on lift shaft 3.

Control valve 13 is provided on the suction side of pump 11 and remains immersed in sump 12. Suction control of pump 11 avoids unnecessary power loss in the pump and the consequent overheating of oil when the system is in the neutral/hold position. An adaptation of the control valve could, however, also be used for provision on the high-pressure side of the pump.

Conduit 14 connects control valve 13 to the sump suction. High-pressure oil from pump 11 is delivered to hydraulic cylinder 1 through conduit 15 for lifting of the lower links 6. Conduit 16 connects hydraulic cylinder 1 to control valve 13 for exhausting the oil in the hydraulic cylinder, the oil flowing through response control" valve 17, so that the speed of lowering of the implements 8 is controlled in accordance with the setting of the response control valve.

Control valve 13 consists of valve body 18 in which slides annular sleeve valve 19. Spool valve 20 in turn slides in this annular sleeve valve 19. Operational condition of the control valve at any instant depends upon the relative position of the spool and annular sleeve valves and 19. Passages 21 and 22 in valve body 18 are connected to the pump suction through conduit 14, and to the hydraulic cylinder 1 through conduit 16 respectively. Communication between drilled ports 23 and 24 on the annular sleeve valve 19 and passages 21 and 22 respectively in the sliding range of the annular sleeve valve 19 is ensured by providing annular grooves 19A on the outer periphery of the annular sleeve valve 19 of the sufficient width. Both the spool valve 20 and the annular valve 19 are urged in the rearward direction S1 by springs 29 and 28 respectively to maintain positive contact with their respective actuating levers. Both ends of the spool valve 20 are open to sump l2 and since the control valve 13 is operated when immersed in sump 12, it always remains filled with oil. Annular sleeve valve 19 is extended forward into fork 25 which engages with oscillating sleeve 26 through pin 27. A eccentric drive, not shown, oscillates the annular sleeve valve 29 through oscillating sleeve 26. The length of the fork 25 is such that pin 27 on oscillating sleeve 26 remains in engagement with the annular sleeve valve 19 in its entire sliding range. This oscillatory motion reduces the friction between the annular sleeve valve 19 and the spool valve 20 on one hand and the an nular sleeve valve 19 and the valve body 18 on the other and improves system sensitivity.

When spool valve 10 is moved in the rearward direction S1, port 24 on the annular sleeve 19 is opened to the sump 12 thus opening cylinder 1 to sump 12 through passage 22 and port 24, effecting lowering of the implement 8 carried by the threepoint linkage. When spool valve 20 is actuated in forward direction S2, port 23 and passage 21 are opened to the sump 12 and oil is allowed into the pump suction through conduit 14 and high-pressure oil is delivered by pump 11 to the hydraulic cylinder 1 through conduit 15 for lifting the lower links 6 and hence the implement 8. The reverse actions respectively take place as the annular sleeve valve 19 is actuated in directions S1 and S2, as is clear from the diagram.

For better system stability ports 23 and 24 in the annular sleeve valve 19 are drilled in a manner that opening of the port passage is gradual.

Operating lever 30 located conveniently for the driver is used for both position and draft control working of the threepoint linkage and for working single-acting external hydraulic cylinders. The complete operating range BE of operating lever on section 31 is subdivided into three working ranges; AB for automatic position control where position A is for transport when working in position control, range AF for external hydraulics and range FE for automatic draft control where position F is the transport position when working in automatic draft control. Adjustable stops 32 and 33 are provided on sector 31 for defining the working limits of the operating lever 30. Operating lever 30 carries profile cam 34 and side cam 35 on its axis. Cam 34 through pivoted link 36 actuates the annular sleeve valve 19. The use of side cam 35 is explained subsequently.

The draft feedback consists of the already mentioned draft sensor spring assembly 9 wherein the control spring 37 measures the magnitude and direction of the forces in upper link 7. Through the forward end of the sensor assembly, draft actuating abutment rod 39 actuated by abutment 38 projects out and its longitudinal position is dependent upon the compressive or tensile forces in the upper link 7. Feedback from draft actuating abutment rod 39 operates draft radial arm 41 through four-bar linkage 40. Similarly the position feedback signal obtained from cam 10 on lift shaft 3 operates position radial arm 44 through roller 43 on four-bar linkage 42. Springs 45 and 46 are provided for the four-bar linkages and 42. Springs and 46 are provided for the four bar linkages 40 and 42 respectively to keep contact with their respective feedback units. Draft and position radial arms 41 and 44 are both mounted freely on hollow central cam spindle 47. Central cam spindle 47 also has central cam 48 mounted freely on it between radial arms 41 and 44. Compression spring 49 fitted between position radial arm 44 and central cam 48 urges the latter towards draft radial arm 41. Central cam 48 carries with it pin 50 fitted to plunger 51, slot 52 in spindle 47 permitting axial movement to the central cam 48 on the spindle 47 in spite of pin 50. Integral groove 53 on central cam 48 permits its free rotation on spindle 47 in spite of pin 50. At the other end of plunger 51 is provided cap 54 loaded by compression spring 55. Lever 56 actuated by side cam 35, actuates plunger 51 through cap 54 and spring 55, the spring and cap arrangement ensuring contact with end of lever 56, the spring providing a give should forward motion of plunger 51 be restrained. Circlip 57 provides the abutment for position are 44 against spring forces. Pins 58 and 59 projecting on opposite sides of central cam 48 engage into either a slot in the draft radial arm 41 or in the position radial arm 44 depending upon the axial position of the central cam 48. Pin 60 on central cam 48 is arranged to lie in the rotational path of draft radial arm 41 irrespective of the axial position of central cam 48. Central cam 48 actuates spool valve 20 through hinged lever 61, contact between lever 61, contact between lever 61 and cam being retained by spring 29 in control valve 13.

Spool valve 62 urged by spring 63 is provided for effecting release of system pressure during overloads and is limited to the neutral position by a stop when it blocks discharge port 64. Ratchet 65 on spool valve 62 can be actuated forward by pawl 66, the pawl-ratchet arrangement providing slip in reverse direction. Pawl 66 is hinged on lever 36 and the lower end of the pawl rests against abutment 68 on lever 67, which runs parallel to lever 36 and on the same hinge point and is spring loaded into contact with cam 34. Corresponding points on levers 67 and 36 therefore have the same movement when under the action of the operating cam 34. The pawl 66 will be actuated downwards when its lower end rests against abutment 68 and lever 36 is actuated forwards, there being downward movement only when there is relative movement between levers 36 and 67. Movement of lever 36 forward separately is caused by abutment 69 on lower 61 coming into contact after a predetermined gap with lever 36, at which stage there is no movement of lever 67 which remains in contact with cam 34 by spring 70. Once the pawl 66 has been actuated downwards into engagement with ratchet 65 on spool valve 20 any further movement of lever 61 causes the spool valve 62 to move forward and open discharge port 64 to sump 12.

Referring to FIG. 8 lever 67 of FIGS. 1 to 7 which runs parallel to lever 36 is eliminated. in this case a differently shaped pawl 66 is actuated downwards by a pin 68a on an extension of lever 61 engaging into a slot in pawl 66. Pawl 66 is actuated downwards when carrying the pawl is stationary and there is any forward motion of lever 61 due to increasing draft forces. Once pawl 66 has been actuated downward into engagement with ratchet 65 on overload relief spool valve 62, any further forward motion of lever 61 causes the forward action of the spool valve 62 to open discharge port 64 to sump 12. Forward motion of lever 36 when actuated by lever 61 is permitted by roller 71 lifting of cam 34 as in the previous system.

The detailed working of the system in various modes of operation will now be described.

AUTOMATIC DRAFT CONTROL For automatic draft control working the operating lever 30 is brought into zone FE of the operating sector where F represents the transport position. The actual operating range for ground-working implement is DE, where movement towards E represents increasing soil drafts. When the operating lever 30 is brought to position F in addition to lifting the implement to transport position the return of the annular sleeve valve 19 and spool valve 20 combination to its neutral position is also ensured.

in range DE when central cam 48 is in its normal position urged towards draft radial arm 41, it rotates rigidly with the draft radial arm 41 through pin connection 58. Pin 59 is then disengaged from position radial arm 44. For working groundengaging engaging implements in the draft control range, operating lever is brought to the required draft setting in range DE at which the implement has to work. This actuates annular sleeve valve 19 in direction S2, establishing connection between the hydraulic cylinder 1 and sump 12 through passage 22 and port 24. Cylinder oil is consequently exhausted and the implement 8 is lowered into the ground. As the tractor moves forward and draft forces increase, compressive forces in upper link 7 are set up and through draft sensor spring assembly 9, abutment 38 and four-bar linkage actuates draft radial arm 41 in the clockwise direction. This in turn moves central cam 48 clockwise which actuates spool valve 20 in direction S2 gradually closing the previously opened exhaust port 24. Port 24 is fully closed when the draft forces exerted by the implement 8 balance the setting corresponding to that of the operating lever 30. Any increase in soil draft forces due to soil variation causes further compressive forces in upper link 7 and through draft sensor spring assembly 9 and central cam 48 actuates spool valve 20 in direction S2. With this movement the pump suction is opened to the sump through port 23 and passage 21. High-pressure oil consequently enters hydraulic cylinder 1 causing the implement 8 to lift. As the implement 8 is being lifted in the soil, draft forces decrease, compressive forces in upper link 7 decrease and the spool valve 20 moves in direction S1. When the compressive forces in the upper link 7 and hence in control spring 37 reach the present value on the operating lever 30 the annular sleeve and spool valve combination attains its neutral position with all ports closed and lifting stops. On the other hand if the draft forces in the upper link 7 decrease the compression in control spring 37 decreases and through the feedback linkage, spool valves 20 is actuated in direction S1 thus opening hydraulic cylinder 1 to sump 12 through conduit 16 passage 22 and the port 24, causing the implement 8 to lower further into the ground, whereafter soil forces increase till the state of balance is achieved with the annular sleeve and spool valve combination regaining its neutral position. Thus irrespective of varying soil conditions, draft forces are maintained at the preset valve corresponding to the setting of the operation lever.

The working of the system for effecting relief of system pressure should the implement strike an obstruction causing an abnormal increase of draft forces is described subsequently.

For lifting the implement to transport position when working in draft control operating lever 30 is brought from its setting somewhere in range DE to position F. This moves annular sleeve valve 19 in direction S1 through cam 34 and lever 36, when the pump suction is opened, which causes the implement 8 to lift. Movement of operating lever 30 from D to F also tends to move central cam 48 towards position radial arm 44 against action of spring 49, through side cam 35, lever 56, cap 54, spring 55, plunger 51 and pin 50. In case the slot on position radial arm 44 is opposite pin 59 on central cam 48 this movement actually takes place bringing central cam 48 into positive connection with and under the control of position radial arm 44. If however, the slot is not opposite pin 59 and the pin comes up against the side of the position radial arm 44, the spring arrangement on plunger 51 provides a give allowing the movement of the operating lever 30 inspite of obstruction to the movement of the central cam 48. Since the position radial arm 44 is rotating anticlockwise with the lifting of the implement, the slot ultimately comes in line with pin 59, when under the action of spring 49, pin 59 and thereby the central cam 48 comes into engagement with position radial arm 44. Thereafter the movement of the central cam 48 comes under central of the position arm 44 and the position control feed back ensures return of the annular sleeve valve 19 to its neutral/hold position'when the implement 8 has risen to the transport position irrespective of the varying weights of implements. This feature ensures the complete closure of the pump suction at the transport position and thereby avoids unnecessary wastage ofpower. POSITION CONTROL For working in position control, operating lever 30 is moved into zone AB of sector 31. A being the transport position and B the lowest. In the zone A to B the pin is no longer connected to draft radial arm 41 and the central cam 48 is in positive connection with position radial arm 44 through pin 59.

Movement of operating lever 30 from A to any position between A and B, moves annular sleeve valve 19 in direction S2 through lever 36, opening port 24 and hence the hydraulic cylinder 1 to sump 12. As the piston 2 draws in, lift shaft 3 rotates anticlockwise and the implement 8 lowers. As the cam 10 on the lift shaft 3 also rotates anticlockwise, position radial arm 44 on the central cam spindle 47 is rotated clockwise through the four-bar linkage 42. This clockwise rotation of position radial arm 44 is followed by central cam 48 and spool valve 20 is actuated in direction S2, progressively closing port 24, which is fully closed when the lift shaft 3 and the implement 8 have moved into a position corresponding to the setting of operating lever 30. For raising the implement 8 reverse action takes place.

OVERLOAD RELEASE During working in draft control if the implement 8 strikes an obstruction and the draft forces increase abnormally, the draft radial arm 41 will move clockwise which will actuate the spool valve 20 in direction S2, causing the implement 8 to lift in the manner described earlier. If however the draft forces still continue to increase and the clockwise rotation of the draft radial arm 41 continues, spool valve 20 continues moving in direction S2, abutment 69 on lever 61 comes into contact with lever 36 and pushes it along, this being permitted by the lifting of roller 71 off cam 34. Since lever 67 remains stationary, relative movement occurs between levers 36 and 67, causing pawl 66 to drop into engagement with ratchet 65 and any further movement of lever 61 causes the opening of the hydraulic circuit to the sump in the manner described earlier which relieves implement weight transfer on to the rear wheels which consequently start spinning. This spin can be noticed by the driver, who can then reverse out of the obstruction. This wheel spin also prevents excessive rearing forces on the tractor which may cause it to overturn.

When working in position control, should overload conditions occur due to obstruction in the manner described earlier, draft radial arm 41, which is not in engagement with the central cam 48 continues moving independently in the clockwise direction till it comes into contact with pin 60 on the central cam 48, whereafter the central cam comes under the control of the draft radial arm 41 and normal working of the overload relief system as in draft control ensures. Since the connection between the central cam 48 and position radial arm 44 is still being maintained, the position radial arm 44 will also be rotated clockwise. This is permitted by the lifting of roller 43 ofi cam 10.

VISUAL CONTROL OF EXTERNAL SINGLE-ACTION RAMS Zone AE on the operating lever sector 31 is used for visual control of single-acting external rams. When between A and F, the drop in the profile of the operating cam 34 moves annular sleeve valve 19 in the direction S1, opening port 23 and hence the pump suction to sump 12, and the pump 11 starts delivering high-pressure fluid. Piston 2 being already at the end of its travel and prevented from further movement by the lift shaft 3 coming against a stop, high-pressure oil flows to lift the external ram and the extent of lift can be visually adjusted by the operator. When the ram has reached the desired height, operating lever 30 is brought into position F, when the pump suction is closed and the spool valve 20/annular sleeve valve 19 combination is in its neutral or hold position. For lowering the ram, operating lever 30 is moved into zone FE, when port 24 in annular sleeve valve 19 is opened and the ram lowers under the effect of gravity.

WORKING OF oouaiE-Acrmo EXTERNAL CYLINDERS For working double-acting external cylinders (not shown in diagrams) the operating lever is moved between positions A and F, when the pump suction is continuously open. Highpressure oil then goes to an auxiliary three-position opencenter spool valve, which can be actuated for working doubleacting external cylinders. Return from the auxiliary valve is connected separately to the tractor sump.

RESPONSE CONTROL The control of the speed of system response to sudden variation in implement loading conditions is provided by variable-orifice response control valve 17 operated by lever 72. Response control is only operative when the implement 8 has to lower down into the soil, when the oil exhausting from the hydraulic cylinder 1 is made to fiow through the variable orifice.

Provisions are available in the system for effecting various adjustments to ensure satisfactory preparation.

We claim:

1. A control mechanism for the regulation of a hydraulic circuit in tractors for controlling the movement and working of mounted implements attached to a three-point linkage, comprising a valve mechanism comprised of at least a first and second control valve controlling the working of the said hydraulic circuit, said second valve disposed within said first control valve, a selection and operational control means for selecting and controlling draftand position-working of the said implement, a draft-sensing means operatively connected to said implement, position-sensing means operatively connected to said implement, and a responsive means arranged to receive an actuation movement from said implement through said draft-sensing means and position-sensing means, said responsive means also arranged to receive an actuation from said selection and operational control means, said responsive means comprising a shaft an actuator rotatably mounted on said shaft. a position member rotatably mounted on said shaft, and arranged to be actuated by said position-sensing means, a draft member rotatably mounted on said shaft and arranged to be actuated by said draft-sensing means, said actuator mounted between said draft member and position member and arranged for engagement with either said position member or draft member upon being actuated by said selection and operational control means, and said actuator being arranged to actuate one of said first and second control valves in response to its engagement with either said position member or draft member.

2. A control mechanism as claimed in claim 1, wherein said actuator comprises a cam.

3. A control mechanism as claimed in claim 2, wherein said position member comprises a position radial arm, and said draft member comprises a draft radial arm.

4. A control mechanism as claimed in claim 3, wherein said shaft being formed as a hollow section, a longitudinal slot provided in said shaft, a spring-loaded plunger disposed within said shaft and having an abutting means arranged to travel within said slot, and said abutting means arranged to actuate said cam upon said plunger being actuated by said selection and control means.

5. A control mechanism as claimed in claim 4, wherein two first pins extending from said cam on the side thereof of the said draft radial arm and one second pin extending from said cam on the side thereof said position radial arm, and spring means urging said cam toward said draft radial arm to maintain engagement of one said first pin on said draft radial arm.

6. A control mechanism as claimed in claim 5, wherein said position radial arm having a slot therein, said abutting means effects the actuation of said cam away from the said draft radial arm into engagement with the position radial arm through said second pin on said cam when said second pin and the slot on said position radial arm are opposite each other, said spring-loaded plunger allowing give in the event the slot in said position radial arm is not opposite said second pin at the moment of actuation and said second pin coming up against the side of said position radial arm, said spring-loaded plunger effecting subsequent engagement of said second pin with the slot when said position radial arm rotates to bring the slot into line with said second pin.

7. A control mechanism as claimed in claim 6, wherein the other said first pin on the said control cam projecting towards said draft radial arm being arranged in the path of the draft radial arm irrespective of the axial position of the said cam, the other said first pin being arranged to actuate said cam when working in automatic position control and the actual draft forces on said implement exceed said draft valve corresponding to the set position by a predetermined amount.

8. A control mechanism as claimed in claim 1, wherein said valve mechanism includes a third valve operative during overload on said implement and capable of receiving an actuation from said responsive means, and said selection and operational means controlling the actuation of said third valve.

9. A control mechanism as claimed in claim 1, wherein the said selection and operational control means include a single operating lever and a plurality of cams on said single operating lever.

10. A control mechanism as claimed in claim 8, wherein said third valve comprising a spool valve located in said hydraulic circuit for selectively releasing the pressure of said hydraulic circuit during overloads in said implement.

11. A control mechanism as claimed in claim 1, wherein said valve mechanism comprises a valve body, said first valve being an annular sleeve valve and cooperating with said second valve and said valve body.

12. A control mechanism as claimed in claim 1, wherein said second valve being a spool valve and cooperates with the said first valve.

13. A control mechanism as claimed in claim 1, wherein the said first and second valves are concentrically arranged.

14. A control mechanism as claimed in claim 1, characterized therein by an oil sump, a pump located in said oil sump, said valve mechanism comprising a valve body containing said first and second valves and said valve mechanism being positioned on the suction side of said pump and immersed and disposed in said oil sump and wherein said first and second valves slide relative to each other and to said valve body.

15. A control mechanism as claimed in claim 14, characterized therein by a profiled first cam, an operating lever mounting said first cam, a first hinged lever arranged to actuate said first valve from said first cam.

16. A control mechanism as claimed in claim 15, wherein a second hinged lever being disposed between said cam and said second valve, and said cam actuating said second valve through said second hinged lever.

17. A control mechanism as claimed in claim 16, wherein spring means being arranged for urging said first and second valves into contact with the respective said first and second levers, and means provided for oscillating said first valve in its entire sliding range.

18. A control mechanism as claimed in claim 1, wherein the said second valve is arranged to be actuated by said responsive means.

19. A control mechanism as claimed in claim 9, wherein a second cam supported on said operating lever for actuating said responsive means.

20. A control mechanism as claimed in claim 16, characterized therein by a third hinged lever hinged at a hinge point adjacent the hinge point of said first hinged lever, said first cam on the said operating lever also arranged to actuate said third hinged lever, and spring means arranged to urge said second hinged lever into contact with said first cam.

21. A control mechanism as claimed in claim 20, characterized therein by a pawl, a second spool valve carrying a ratchet, said ratchet coming into engagement with said pawl having a downwardly motion, whereby subsequent actuation of said pawl effecting movement of said spool valve to relieve the pressure in said hydraulic circuit.

22. A control mechanism as claimed in claim 21, characterized therein by a pin carrying said pawl on said first hinged lever operating the said first valve, an abutment on said third hinged lever, the opposite end of said pawl spaced from said pin resting against said abutment on said third lever, so that downward motion of said pawl occurs only when said third hinged lever moves relatively to said first hinged lever.

23. A control mechanism as claimed in claim 22, characterized therein by an abutment on said second hinged lever, the relative motion causing the downward actuation of the pawl occuring when said abutment on said second hinged lever operating said second valve comes up against and carries forward with its said first hinged lever actuating said first valve with said third hinged lever remaining stationary, any further forward motion of the said abutment causing forward movement of the said spool valve carrying the said ratchet.

24. A control mechanism as claimed in claim 1, characterized therein by a first lever and a second lever, a spool valve, a ratchet secured to said spool valve, a pawl mounted on said first lever and arranged to be contacted by said ratchet and having a slot therein, said second lever having a pin thereon arranged to engage in he slot in said pawl, wherein the pressure in said hydraulic circuit is relieved whenever the draft forces on said implement increases substantially and with the relief being effected through said second spool valve.

25. A control mechanism as claimed in claim 15, characterized therein by a single-acting external hydraulic cylinder, said first cam on said operating lever being profiled for control of said single-acting external hydraulic cylinders.

26. A control mechanism as claimed in claim 1, wherein an independently controlled infinitely variable orifice valve being provided in the discharge line of said hydraulic circuit. 

1. A control mechanism for the regulation of a hydraulic circuit in tractors for controlling the movement and working of mounted implements attached to a three-point linkage, comprising a valve mechanism comprised of at least a first and second control valve controlling the working of the said hydraulic circuit, said second valve disposed within said first control valve, a selection and operational control means for selecting and controlling draft- and position-working of the said implement, a draft-sensIng means operatively connected to said implement, position-sensing means operatively connected to said implement, and a responsive means arranged to receive an actuation movement from said implement through said draft-sensing means and position-sensing means, said responsive means also arranged to receive an actuation from said selection and operational control means, said responsive means comprising a shaft an actuator rotatably mounted on said shaft. a position member rotatably mounted on said shaft, and arranged to be actuated by said position-sensing means, a draft member rotatably mounted on said shaft and arranged to be actuated by said draft-sensing means, said actuator mounted between said draft member and position member and arranged for engagement with either said position member or draft member upon being actuated by said selection and operational control means, and said actuator being arranged to actuate one of said first and second control valves in response to its engagement with either said position member or draft member.
 2. A control mechanism as claimed in claim 1, wherein said actuator comprises a cam.
 3. A control mechanism as claimed in claim 2, wherein said position member comprises a position radial arm, and said draft member comprises a draft radial arm.
 4. A control mechanism as claimed in claim 3, wherein said shaft being formed as a hollow section, a longitudinal slot provided in said shaft, a spring-loaded plunger disposed within said shaft and having an abutting means arranged to travel within said slot, and said abutting means arranged to actuate said cam upon said plunger being actuated by said selection and control means.
 5. A control mechanism as claimed in claim 4, wherein two first pins extending from said cam on the side thereof of the said draft radial arm and one second pin extending from said cam on the side thereof said position radial arm, and spring means urging said cam toward said draft radial arm to maintain engagement of one said first pin on said draft radial arm.
 6. A control mechanism as claimed in claim 5, wherein said position radial arm having a slot therein, said abutting means effects the actuation of said cam away from the said draft radial arm into engagement with the position radial arm through said second pin on said cam when said second pin and the slot on said position radial arm are opposite each other, said spring-loaded plunger allowing give in the event the slot in said position radial arm is not opposite said second pin at the moment of actuation and said second pin coming up against the side of said position radial arm, said spring-loaded plunger effecting subsequent engagement of said second pin with the slot when said position radial arm rotates to bring the slot into line with said second pin.
 7. A control mechanism as claimed in claim 6, wherein the other said first pin on the said control cam projecting towards said draft radial arm being arranged in the path of the draft radial arm irrespective of the axial position of the said cam, the other said first pin being arranged to actuate said cam when working in automatic position control and the actual draft forces on said implement exceed said draft valve corresponding to the set position by a predetermined amount.
 8. A control mechanism as claimed in claim 1, wherein said valve mechanism includes a third valve operative during overload on said implement and capable of receiving an actuation from said responsive means, and said selection and operational means controlling the actuation of said third valve.
 9. A control mechanism as claimed in claim 1, wherein the said selection and operational control means include a single operating lever and a plurality of cams on said single operating lever.
 10. A control mechanism as claimed in claim 8, wherein said third valve comprising a spool valve located in said hydraulic circuit for selectively releasing the pressure of said hydraulic circuit during overloads in said implement.
 11. A control mechanism as claimed in claim 1, wherein said valve mechanism comprises a valve body, said first valve being an annular sleeve valve and cooperating with said second valve and said valve body.
 12. A control mechanism as claimed in claim 1, wherein said second valve being a spool valve and cooperates with the said first valve.
 13. A control mechanism as claimed in claim 1, wherein the said first and second valves are concentrically arranged.
 14. A control mechanism as claimed in claim 1, characterized therein by an oil sump, a pump located in said oil sump, said valve mechanism comprising a valve body containing said first and second valves and said valve mechanism being positioned on the suction side of said pump and immersed and disposed in said oil sump and wherein said first and second valves slide relative to each other and to said valve body.
 15. A control mechanism as claimed in claim 14, characterized therein by a profiled first cam, an operating lever mounting said first cam, a first hinged lever arranged to actuate said first valve from said first cam.
 16. A control mechanism as claimed in claim 15, wherein a second hinged lever being disposed between said cam and said second valve, and said cam actuating said second valve through said second hinged lever.
 17. A control mechanism as claimed in claim 16, wherein spring means being arranged for urging said first and second valves into contact with the respective said first and second levers, and means provided for oscillating said first valve in its entire sliding range.
 18. A control mechanism as claimed in claim 1, wherein the said second valve is arranged to be actuated by said responsive means.
 19. A control mechanism as claimed in claim 9, wherein a second cam supported on said operating lever for actuating said responsive means.
 20. A control mechanism as claimed in claim 16, characterized therein by a third hinged lever hinged at a hinge point adjacent the hinge point of said first hinged lever, said first cam on the said operating lever also arranged to actuate said third hinged lever, and spring means arranged to urge said second hinged lever into contact with said first cam.
 21. A control mechanism as claimed in claim 20, characterized therein by a pawl, a second spool valve carrying a ratchet, said ratchet coming into engagement with said pawl having a downwardly motion, whereby subsequent actuation of said pawl effecting movement of said spool valve to relieve the pressure in said hydraulic circuit.
 22. A control mechanism as claimed in claim 21, characterized therein by a pin carrying said pawl on said first hinged lever operating the said first valve, an abutment on said third hinged lever, the opposite end of said pawl spaced from said pin resting against said abutment on said third lever, so that downward motion of said pawl occurs only when said third hinged lever moves relatively to said first hinged lever.
 23. A control mechanism as claimed in claim 22, characterized therein by an abutment on said second hinged lever, the relative motion causing the downward actuation of the pawl occuring when said abutment on said second hinged lever operating said second valve comes up against and carries forward with its said first hinged lever actuating said first valve with said third hinged lever remaining stationary, any further forward motion of the said abutment causing forward movement of the said spool valve carrying the said ratchet.
 24. A control mechanism as claimed in claim 1, characterized therein by a first lever and a second lever, a spool valve, a ratchet secured to said spool valve, a pawl mounted on said first lever and arranged to be contacted by said ratchet and having a slot therein, said second lever having a pin thereon arranged to engage in he slot in said pawl, wherein the pressure in said hydraulic circuit is relieved whenever the draft forces on said implement increases substantially and with the relief being effected through said second spool valve.
 25. A control mechanism as claimed in claim 15, characterized therein by a single-acting external hydraulic cylinder, said first cam on said operating lever being profiled for control of said single-acting external hydraulic cylinders.
 26. A control mechanism as claimed in claim 1, wherein an independently controlled infinitely variable orifice valve being provided in the discharge line of said hydraulic circuit. 